Various digital mobile phone standards are currently deployed worldwide. These standards include, for example, Global System for Mobile Communications (GSM) and Universal Mobile Telecommunications Service (UMTS) in Europe and (Code-Division Multiple Access) CDMA in the United States. Due to the increasing demand for mobile telephone services, many of these standards are deployed together. In addition, further deployments of new standards are currently underway or will be in the foreseeable future. For example, the Long Term Evolution (LTE) standard and the IEEE 802.16 (WiMax) standard are currently being deployed.
In the transition from the currently deployed standards (second generation) to the third or fourth generation standards, both second and third generation standards currently coexist and will continue to do so for the foreseeable future. Thus, multi-frequency band systems, that include two or more frequency bands belonging to two or more communication standards will continue to coexist in parallel and will work together to provide coverage and services to the wireless communications devices.
Many new frequency bands have been deployed for use and operators are requesting increased roaming capability. Roaming is a general term referring to the extension of connectivity service in a location that is different from a home location where the service was registered. Roaming typical increases the likelihood that the wireless communications device is connected to the network, without losing the connection. Thus, there is now a demand for wireless communications devices to support more than one frequency band. For example, legacy GSM/Enhanced Data GSM Environment (EDGE) may be required on overlapping Wideband Code-Division Multiple Access (WCDMA) frequency bands, such as GSM850/WCDMA B5 and GSM900/WCDMA B8.
To comply with both the demand for more functionality in the wireless communications device as well as the decreased size of the wireless communications device, conventional wireless communications devices re-use filters for the GSM path, which is called co-banding, i.e, the filters are reused for the same frequency. Since WCDMA is a full duplex system (can transmit/receive data in two directions simultaneously), a duplex filter is used for WCDMA, which has a higher insertion loss than a single receive filter. Thus, improved methods of co-banding are desired.